更改java.util.List的输出类型

Question

I created this example:

List<Integer> list = new ArrayList<Integer>();
for(int i = 0; i < 10; i++) {
   list.add(new Random().nextInt(30) + 1);
}
System.out.println(list);

Output:

[13, 9, 20, 3, 8, 29, 13, 11, 9, 16]  // array shape

Why the List 's output always print array shape with square bracket !!

My Question : Can I change type of the output like this 13 9 20 3 8 29 13 11 9 16 or another shape ?

Answer 1

You can do it using Regular Expressions but I'm not an expert.

Here is another way to customize your list's output.

Create a method that takes a list as a parameter and outputs a String.

public static void main(String[] args) throws java.lang.Exception {
    List<Integer> list = new ArrayList<Integer>();
    for(int i = 0; i < 10; i++) {
       list.add(new Random().nextInt(30) + 1);
    }
    System.out.println(formatMyList(list));
}

public static String formatMyList(List list){
    String str = list.toString().replace("[", "{");
    str = str.replace("]", "}");
    str = str.replace(",", " -");
    return str;
}

Output :

{25 - 20 - 12 - 25 - 18 - 11 - 17 - 23 - 22 - 29}

---

You can also customize :

   public static String formatMyList(List list){
        String str = list.toString().replace("[", "I GOT ");
        str = str.replace("]", "!");
        str = str.replace(",", " AND");
        return str;
    }

Output :

I GOT 18 AND 22 AND 14 AND 16 AND 22 AND 21 AND 7 AND 14 AND 21 AND 14!

Answer 2

I would use a StringBuilder

StringBuilder sb = new StringBuilder();

for (int i: list) {
    sb.append(i + "\t");
}

System.out.println(sb.toString().trim());  //trim() to remove the last \t

Output:

11 10 29 9 12 13 17 28 19 3